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Eight investigational sites are involved in clinical trials of the 3M/House cochlear implant for children. Statistical analyses have been performed to examine differences between investigators in patient populations selected for implantation and in the results achieved. Important characteristics of the subjects from different investigational sites were compared for House, Maddox, and all "others" combined. There were no differences between investigators in sex, age at surgery, or duration of deafness of the children enrolled in the study. For age at onset, House and Others had higher proportions of postlingually deaf subjects than Maddox (16% for House and 18% for Others, compared with less than 2% for Maddox). However, all investigators had some subjects in every category: postlingual, prelingual, and congenital. Auditory discrimination and speech production scores for subjects from the three groups were compared using analysis of variance techniques. A few interaction effects between time interval and investigator indicated that not all investigator groups performed similarly over time for all measures. However, postimplant scores were always significantly higher than preimplant scores for all investigators. Differences that did occur appeared to be attributable to differences in subject characteristics.